title: Observation of room-temperature ballistic thermal conduction persisting over 8.3 µm in SiGe nanowires.
abstract: In ballistic thermal conduction, the wave characteristics of phonons allow the transmission of energy without dissipation. However, the observation of ballistic heat transport at room temperature is challenging because of the short phonon mean free path. Here we show that ballistic thermal conduction persisting over 8.3 µm can be observed in SiGe nanowires with low thermal conductivity for a wide range of structural variations and alloy concentrations. We find that an unexpectedly low percentage (∼0.04%) of phonons carry out the heat conduction process in SiGe nanowires, and that the ballistic phonons display properties including non-additive thermal resistances in series, unconventional contact thermal resistance, and unusual robustness against external perturbations. These results, obtained in a model semiconductor, could enable wave-engineering of phonons and help to realize heat waveguides, terahertz phononic crystals and quantum phononic/thermoelectric devices ready to be integrated into existing silicon-based electronics.
authors.affiliation: Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan.
authors.forename: Tzu-Kan
authors.initials: TK
authors.lastname: Hsiao
authors.forename: Hsu-Kai
authors.initials: HK
authors.lastname: Chang
authors.forename: Sz-Chian
authors.initials: SC
authors.lastname: Liou
authors.forename: Ming-Wen
authors.initials: MW
authors.lastname: Chu
authors.forename: Si-Chen
authors.initials: SC
authors.lastname: Lee
authors.forename: Chih-Wei
authors.initials: CW
authors.lastname: Chang